Nowadays, a complementary metal oxide semiconductor image sensor (CMOS image sensor for short) mainly includes an analog signal processing module and a digital signal processing module. Specifically, the CMOS image sensor includes pixel units, a control circuit, an analog front-end processing circuit, an A/D converter, an image signal processing circuit and a related storage unit, etc. With the development of the CMOS image sensor, the research on the CMOS image sensor is more and more in-depth, and the performance of the CMOS image sensor is significantly improved. However, due to an process structure of the CMOS image sensor and the CMOS image sensor itself, when the light is too bright, a voltage of the reset sampling signal of the image sensor reduces, and when the light brightness is larger than a predetermined value, the voltage of the reset sampling signal of the image sensor reduces more quickly with the increment of the light brightness, such that a sunspot occurs for the image sensor when the light brightness is larger. For example, when taking a photo towards the sun, a certain range of sunspots occurs in the photo.
In the related art, there are two ways for removing the sunspot. In the first way, the sunspot is removed in a digital way: first, it is determined whether a sunspot phenomenon occurs, and when it is determined that the sunspot phenomenon occurs, a compensation is performed on the sunspot area, that is, a brightness value in the sunspot area is adjusted to be the same with the that around the sunspot area. In the second way, the sunspot is removed in an analog way: first, it is determined whether the sunspot phenomenon occurs, that is, it is determined whether a difference between a reset sampling level and a reference level is larger than a predetermined value, and when it is determined that the sunspot phenomenon occurs (the difference is larger than the predetermined value), the reset sampling level is replaced with a fixed level generated by a fixed level generation circuit, so as to correct the sunspot phenomenon caused by the reduction of the reset sampling level.
The ways for removing the sunspot in the related art at least have following disadvantages.
1. With the digital way, it is easy to misjudge the sunspot, that is, the judgment about whether there is the sunspot phenomenon is inaccurate. For example, a black object may be misjudged to be the sunspot, since the form of the black object is similar to the sunspot. Moreover, the sunspot may not be judged accurately, for example, the sunspot may be considered as the black object.
2. With the analog way which replaces the reset sampling level with the fixed level generated by the fixed level generation circuit, although no misjudgment will be made, too much noise will be caused to the sampling circuit.